1. Field of the Invention
The present invention relates to a battery charging device for charging batteries of electric vehicles by selective use of a high-voltage or low-voltage electric power source outside the vehicle.
2. Description of Background Art
Efforts have been made in recent years to develop electric vehicles in the hope of building transportation means free of environmental pollution, however, many problems, especially concerning batteries, must be solved before realizing a wide spread of the electric vehicles.
Namely, a high-voltage battery is necessary to realize a practical electric vehicle running with electric power of a battery, or a battery of a large capacity is necessary to enable an electric vehicle a long distance drive. In addition, the electric vehicle is equipped with various auxiliary electric equipment necessary for driving, which must be supplied with electric power.
There has been proposed a high-voltage supply system including a DC-DC converter equipped between a battery and a driving motor of an electric vehicle for supplying an increased voltage to the driving motor by converting a low-voltage of the battery to a high-voltage (for instance, Japanese Laid-Open Patent publication No. 63-194568). There has also been proposed a low-voltage supply system in which a high-voltage of the battery is decreased to a low-voltage by a DC-DC converter for supplying auxiliary electric equipment with a low-voltage electric power (for instance, Japanese Laid-Open Patent Publication No. 57-211946).
For the purpose of realizing a long-distance drive by an electric vehicle, it will be necessary to equip the vehicle with a large capacity battery, or to provided electric power supply stations for electric vehicles over a wide area. However, different from vehicles running by gasoline for which many gasoline stations have been provided all over the land, the number of electric power supply stations available for electric vehicles is possibly limited. On the other hand, it is possible to provide the vehicle with a supplemental battery besides a main battery, however, this solution will also be improper because such a supplemental battery may cause an increased weight of the vehicle.